Construction methods using cementitious grouting materials are being employed not only in foundation of dams, prevention of ground liquefaction, and reinforcement of rock and ground in tunnel excavation, but also in water cut-off treatments in energy-related facilities, industrial waste disposal facilities, and underground structures in urban civil engineering, recently.
As cementitious grouting materials, for grouting into little-permeable ground or for extending the effect of grouting to large area, ultrafine particles grouting materials having a maximum particle size of 10 to 20 μm obtained by pulverizing and classifying a mixture consisting of blast-furnace slag mainly and Portland cement are used, and there are many examples using such materials. (e.g., see Patent Document 1).
Ultrafine particle grouting materials having a fine particle size has strong cohesive property. Due to the apparent particle size, which is coarsened through coagulation, expected grouting effects often fail to be exhibited. For this reason, high-level dispersion of particles is required. As such dispersion, a retardation-type high-performance water-reducing agent is widely used (Patent Document 2).
The amount of a retardation-type high-performance water-reducing agent required for high dispersion of an ultrafine particle grouting material in the grout slurry is relatively much compared with the amount used in concrete or mortar. So hard set and hardening of a high-viscosity dehydrated cake of injected grout are markedly retarded. It takes 10 hours for a dehydrated cake to be hard set even when non-retarding type dispersion agent is used, and 20 to 40 hours when a retarder-type is used, in some cases.
A dehydrated cake of injected grout may fail to obtain sufficient effects of the grouting material in a case either where it receives an external force before setting or hardening or where it contacts with confined water or running water to be removed and washed away from the ground therein. And also if hardening of the dehydrated cake is markedly delayed, the whole construction process including the step next to grouting is disturbed, which may lead to economical disadvantages.
On the other hand, as a grouting for limited area, a grouting material composition using a specific high performance water reducing agent or an inorganic sulfuric acid salt is devised for the purpose of shortening the setting time (Patent Document 3). Such a grouting material has, however, problems that setting and hardening are insufficient and that due to high hydration rate, injectability decreases.    [Patent Document 1] Japanese Patent No. 2894529    [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-49164    [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-231884